The invention relates to a screw-type compressor with a primary rotor assembly shaft on which at least a first and a second primary rotor are arranged, respectively meshing with a matching first and second secondary rotor on a secondary rotor assembly shaft.
To compress gaseous matter such as air and to make it available as compressed gas, screw-type compressors are used. These screw-type compressors must be adapted to the operative conditions of the gas to be compressed, it being of particular importance to provide the gas in a desired amount and with a desired pressure. Moreover, requirements concerning the purity of the gas are often made so that oil lubrication may sometimes be undesirable.
The amount of compressed gas and the gas pressure obtainable with the screw-type compressor depend on the rotor geometry of the rotors used in the screw-type compressor and the rotational speed of the rotors. However, it has been found that due to the peripheral velocities occurring at the rotor circumference and due to sealing problems between the rotors of a screw-type compressor stage, the possibilities of increasing the rotational speed and the rotor diameter are limited.
To avoid restrictions in the amount of compressed gas delivered by the screw-type compressor, one has developed screw-type compressors with double-helical gearing having two rotors on the primary rotor assembly shaft and the secondary rotor assembly shaft, respectively, with which the amount of compressed gas delivered by the screw-type compressor could be increased.
Such a double-screw compressor is known from DE 30 31 801 A1. This screw-type compressor has primary rotors with leftward and rightward helical screws, arranged on a common shaft adjoining each other at the end faces in a joining plane and meshing with corresponding leftward and rightward helical secondary rotors also arranged on a common shaft and adjoining each other at the end faces. In this screw-type compressor, the gaseous medium to be compressed is transported to the center of the screw-type compressor, from where it is let out in the radial direction. To avoid the effect known as the "enclosed pocket" and to guarantee a good transport of the compressed gas, the two rotor pairs are angularly offset with respect to each other so that the enclosed pocket of the one rotor pair that is forming may be vented into the still open helical groove of the trailing opposite rotor pair. Since the rotor pairs abut at their centers, the primary and secondary rotor assembly shafts are each supported at their opposite outer ends.
However, due to the overflow of the compressed gas, the known screw-type compressor has an unsatisfactory efficiency. Moreover, the supporting of the primary and secondary rotor assembly shafts is expensive, since the forces occurring at the rotors cause a complex load characteristic of the primary and secondary assembly rotor shaft, both in the radial and the axial directions, resulting in high wear.